Congolese general and former presidential candidate Jean-Marie Michel Mokoko, 71, was sentenced on Friday to 20 years for "undermining internal state security" after authorities accused him of trying to stage a coup.
"The criminal court declares Jean-Marie Michel Mokoko guilty of the facts charged to him," criminal court president Christian Oba said.
Seven co-defendants -- six French and a Congolese -- were sentenced in absentia to the same prison term.
Mokoko, 71 and a former chief of staff of the Republic of Congo's army, has three days to appeal his conviction for undermining state security following the 2016 election in which he placed third.
The defence counsel for the general, who was once an advisor of long-serving President Denis Sassou Nguesso, had said the trial was "simply a settling of political scores."
In March 2016, Mokoko won less than a 14% vote share as Sassou Nguesso was controversially declared a first-round winner.
Sassou Nguesso, 74, has cumulatively spent almost 35 years in office since 1979.
After the vote, Mokoko and other candidates called for a campaign of "civil disobedience."
But "had he wanted to stage a coup he would have done so a long time ago. General Jean-Marie Michel Mokoko never said 'take up arms'," one of his lawyers, Norbert Tricaud, told RFI on Thursday.
"The decision of the criminal court doesn't surprise us because (the case) all began illegally in violation of our client's judicial immunity," Mokoko's lawyer, Eric Yvon Ibouanga said after the court handed down its decision.
The prosecuting team had refused the defence claim that Mokoko was entitled to immunity as a "dignitary of the Republic".
French lawyer Gerard Deviller, part of the state's prosecution team, said that punishment was merited "given the seriousness of the offence".